It is the photograph that adorns student bedsits across the world. The famed black and white portrait of Ernesto "Che" Guevara perfectly captured his intense stare and brooding good looks, helping establish his myth. But exactly 50 years since Cuban photographer Alberto Díaz "Korda" Gutiérrez snapped the Marxist revolutionary, the image has become the subject of bitter legal battles.

Since Korda's death in 2001, his daughter, Diana Díaz, has pursued companies she accuses of breaching the photograph's copyright by using it in their advertising campaigns. Her father employed a similar tactic when he sued Smirnoff Vodka for the illegal use of the image in 2001, a case that re-established his copyright after 41 years.

Díaz's legal battles are not without controversy – or irony. For decades the Argentinian-born Guevara's adopted spiritual home of Cuba did not recognise copyright. It was only following the collapse of the former Soviet Union that Cuba joined the World Trade Organisation and legalised copyright.

Díaz, who lives in Cuba, says that to fund her legal battles she has had to sell licences to a range of "Che" products, including baseball caps, T-shirts and, of course, berets. Her control of the Che brand has led to reports of rows with her half-siblings who live in exile.

The fact that the photograph, taken with a Leica camera on 4 March 1960 at a political rally in Havana attended by Jean-Paul Sartre and Simone de Beauvoir, came to international prominence owes as much to luck as Korda's skill. "It was not planned, it was intuitive," said Korda, who worked for the Revolución newspaper. He told one interviewer that Guevara had shown such an intense gaze that he had been briefly taken aback and only managed to fire off two quick shots, one vertical, one horizontal.

It was at the same rally that Cuban leader Fidel Castro delivered his famous "Homeland or Death" slogan in front of thousands of people. But the photograph of Guevara, which Korda later called "Heroic Guerrilla", did not make the next day's paper and only emerged after Guevara's death in Bolivia seven years later.

Korda, a Porsche-driving fashion photographer who had become infatuated with Castro's Cuba, admitted that he cropped the original shot to make Guevara's gaze stand out.

In the decades that followed, it became a template for myriad other photographs and has been widely copied by political strategists keen to promote their candidate. It has been claimed that Barack Obama's "Hope" poster during his presidential campaign was heavily influenced by Korda's work.

The fact that for many years it was not under copyright meant the image could be utilised by whoever wanted it, something that ensured its ubiquity. Interest in Korda's work remains strong and prices for his iconic prints are rising at auction. Another Korda photograph of Guevara, this time of him fishing, went for £6,600, three times its asking price, at a sale in Gloucestershire this month. The signed Korda print was part of a collection acquired after his death. Other pictures in the sale showed Castro playing golf and meeting Ernest Hemingway.

Michael Casey, the author of Che's Afterlife: The Legacy of an Image, notes the irony that the Marxist's photo is now a marketing weapon. "But the truth is entirely consistent with the realities of our post-Cold War world," Casey writes. "As Cuba has demonstrated, 'revolution' is a brand, not a goal in itself."

Korda justified the copyright lawsuits he brought as his way of protecting Cuba's socialist principles.